The broad philosophical project of naturalism can be extended to theories of scientific methodology. Initially it might seem implausible that normative matters, whether of rationality and principles of method or of morality, should find a place within any kind of philosophical naturalism, which, on the face of it, is non-normative in character. So, what is naturalism and how does it resolve this prima facie problem? Naturalism comes in two broad varieties, metaphysical (or ontological) and methodological. The metaphysical doctrine can be expressed in various ways. The first way is that the only entities that exist are those that have a location within the spacetime system; there are no entities outside it. A second way is that what exists is whatever is postulated in the various sciences such as electromagnetic waves, dna, pulsars or the sociologist's anomie. Some argue that numbers and sets are ineliminable postulates of mathematics used in science, and then they point out that numbers and sets are abstract objects and are not locatable within the spacetime framework; so the second kind of naturalism must be broader than the first and contains abstract items outside the spatiotemporal. Here we need not enter into disputes about the more precise characterization of metaphysical naturalism.